Can Famotidine Cause Constipation?
Yes, famotidine can cause constipation, though it occurs in a relatively small proportion of patients—constipation was reported in ≥1% of famotidine-treated patients in clinical trials. 1
Evidence from Clinical Trials
The FDA-approved drug label for famotidine, based on clinical trials involving approximately 2,500 patients, identifies constipation as one of the adverse reactions occurring in ≥1% of treated patients. 1 This places constipation among the more common side effects alongside headache and dizziness. 1
Clinical Context and Frequency
In the pivotal clinical trials, 1,442 patients received famotidine at various dosing regimens (20 mg once daily, 20 mg twice daily, 40 mg once daily, and 40 mg twice daily). 1
The population studied was broadly representative (ages 17-91 years, distributed across genders and races, predominantly Caucasian). 1
While constipation is listed as occurring in ≥1% of patients, the exact incidence rate was not specified in the FDA labeling, suggesting it is relatively uncommon but clinically recognized. 1
Comparison to Other Gastrointestinal Effects
Famotidine's gastrointestinal adverse effect profile also includes less common reactions (<1% incidence) such as vomiting, nausea, abdominal discomfort, anorexia, and dry mouth. 1 The fact that constipation reached the ≥1% threshold while these other GI symptoms did not suggests constipation may be slightly more prevalent among famotidine's gastrointestinal side effects.
Important Clinical Considerations
Tolerability: Multiple large-scale analyses confirm that famotidine is generally well tolerated, with adverse effects being uncommon across all dosing regimens studied. 2
Discontinuation rates: In multicenter studies of over 2,600 patients, adverse effects led to therapy discontinuation in only three patients (two due to rash, one due to dizziness)—notably, none discontinued due to constipation. 2
No dose-related pattern: The three main dosing regimens studied (20 mg twice daily, 40 mg at bedtime, and 40 mg twice daily) showed no significant differences in side effect profiles, including constipation. 2
Mechanism and Management
While the provided evidence does not detail the mechanism by which famotidine causes constipation, H2-receptor antagonists as a class can affect gastrointestinal motility. If constipation develops during famotidine therapy, standard management approaches (increased fluid intake, dietary fiber, physical activity) should be considered before discontinuing an otherwise effective medication.